Patent GB-724651-A (GB)
Title: Improvements in or relating to photographic roller blind shutters
IPC: G03B9/32
Filed: 1953-01-14
Abstract: 724,651. Photographic .roller blind shutters. BEISLY, F. E. Jan. 14, 1963, No. 1054/63. Class 98 (1). In a self-capping roller blind shutter having two spring-driven blinds and in which continued winding of the closing blind, which is positively connected to the winding mechanism, after the opening blind is set determines the exposure time, a friction clutch is disposed between the opening blind and the winding mechanism and is adapted to prevent exposure movement of the opening blind whilst the closing blind is being set and a unidirectional clutch is disposed between the opening blind and the winding mechanism to allow the closing blind to be drawn from its set position by its spring with the opening blind in its fully withdrawn position without otherwise disconnecting the winding mechanism from either blind. As shown, the shutter is in the rest position where the rear portion 12 of the second or closing blind covers the exposure aperture 14 and the similar aperture in this blind, defined by marginal tapes joining the portion 12 to a forward portion, is closed by the first or opening blind 10, one end of the second blind being wound on a winding roller 5 and the other on a spring roller 4 while the tapes 11 of the first blind are wound on a winding roller 9 and the blind itself is wound on a spring roller 8. On rotating anticlockwise the setting knob 19 which has a pin on a collar 60 engageable in a selected one of a number of holes 55 in a gearwheel 18 on a shaft 53, the two blinds are wound simultaneously in capping relation across the aperture 14 by teeth 17 on the gear 18 engaging pinions 16, 20 on the shafts 3, 7 of the winding pinions 16, 20 on the shafts 3, 7 of the winding rollers 5, 9. When the first blind 10 covers the aperture 14, it is fully unwound from the roller 8 so that further rotation of the roller 9 is prevented. As a result slip occurs in a friction clutch comprising a helical spring 48 bearing against the inner surface of the roller- and located on a boss 49 on a disc 46 connected by an inwardly urged ratchet pawl 44 to a ratchet wheel 43 fixed on the shaft 7. Further rotation of the knob then winds on only the second blind to an extent limited by engagement with a fixed stop 57 of a pin 56 on the collar 50 of the knob, the angular position of the pin 56 having been set by rotating the knob 19 about the shaft 53 to bring a chosen exposure time scale mark against a fixed mark on the shaft thereby determining the width of the exposure slot between the trailing edges of the blinds, whereupon the shutter is held set by a ratchet pawl 26 engaging teeth 23 on the wheel 18. On pressing the lever 24, the pawl is disengaged and the gear teeth 17 ensure that the two blinds run down together to effect an exposure with a substantially fixed slot width. When the first blind has been wound completely on to its spring roller, continued rotation of the shaft 7 may continue due to the pawl 44 slipping over the teeth of the ratchet wheel 43 so that the wheel 18 and roller 5 may continue to rotate and allow the spring roller 4 to wind the second blind into the closing rest position where the shutter is arrested by a pin 21 on the wheel 18 engaging a fixed stop 22. For time exposures, the second blind is wound up so that the leading edge of its aperture registers with the trailing edge of the first blind and the guide 41 is slid upwards by means of a handle 63 as seen in Fig. 3. On pressing the lever 24, the pawl 26 frees the shutter but the end 38 of a link 39 engages a flange 36 on a pivoted lever 33 and moves it clockwise against a spring to bring a nose 37 into the path of a pin 35 on the gear 18 so that the second shutter blind is arrested with its aperture opening the whole shutter aperture. At this point, a mutilated portion 42 in the teeth 23 is opposite the pawl 26 so that, while on releasing the trigger the nose 37 frees thepin 35, the shutter moves only a small distance since the pawl 26 engages the first tooth past the mutilated portion so that the shutter remains open. To close the shutter, the lever 24 is again pressed disengaging the pawl 26 so that the wheel 18 rotates to allow the second blind to return to rest, the pin 35 having already moved beyond the nose 37.